Structural analysis of some molten materials by X-ray diffraction. Part 2.—Li2SO4, Na2SO4 and the mixed system

Abstract

The structures of molten Li₂SO₄, Na₂SO₄ and their mixtures have been examined by consideration of the radial distribution function and the molar volume. The existence of tetrahedral sulphate ions in these molten salts has been demonstrated. S—O and O—O distances for the sulphate ion in the molten state are 1.50₀ and 2.45₀Å, respectively. A close packed arrangement of sulphate ions appears to be the configuration realized in molten Li₂SO₄; the calculated correlation function based on this structural model is qualitatively in good agreement with the observed one. In molten Na₂SO₄, sodium ions probably occupy a position intermediate between the edge and face sites of the sulphate ion; the nearest-neighbour distances of Na—S and Na—O pairs are 2.8 and 2.33 Å, respectively.